Indicate which detector triggered the HotwordDetectionService

Currently we are adding the metrics to find why there is a significant
drop in assistant successful queries for using trusted hotword. In the
metrics, we need to know which detector is used. In this patch, we
first provide the way to distinguish which detector triggered the
HotwordDetectionService.

Bug: 215633663
Test: atest CtsVoiceInteractionTestCases
Test: atest CtsVoiceInteractionTestCases --instant
Change-Id: I2fa904c5a52d714c9ecb545084ffb60e81ed1d8a